From what I can tell, there isn't much difference. My guess is the developer was making up for the lack of this functionality in Django 1.3 and didn't realize that 1.4 added it. Before 1.4, django pipeline was a good solution but was difficult to work with IMO. Glad to see this included in 1.4 for sure.
The difference is this just appends the hash to the url, the builtin actually saves the static file with the hash in the file name.